The cost to fix a low oil pressure situation in your vehicle will depend on the actual cause of the oil pressure being low.
The low oil pressure could be as simple as the engine oil level being low and adding some oil to raise the oil level can then increase the oil pressure.
Another cause could be worn out engine bearings that are increasing the clearances on the crankshaft which then causes the oil to go through the bearings to easily.
Or you could have a bad oil pump which is not very common but possible.
The first few things I would check is the oil level and also the oil pressure sender because the oil pressure sender can go bad and cause a low oil pressure reading when in fact you have good oil pressure.
You should hook up a good mechanical oil pressure gauge to determine if you do have low oil pressure or not.
The new oil pressure sender can be between $20.00 to $40.00 depending on the vehicle.
If you need new bearings or an oil pump then the cost could be as high as $200.00 to $500.00 because replacing the engine bearings requires removing the engine and engine oil pan.
If it's the bearings you are usually better off either getting a new car or getting another engine.
Your oil pressure should be a minimum of 15 to 25 PSI when idling and 40 to 60 PSI when driving.